“Solid heat transfer element” is a term used to describe heat transfer bodies that are in contact with one fluid flow at a time and are solid in the center. For example, one known type of solid heat transfer element is resistance heating wire where the heat is created by electricity passing through electrically resistive material. Another type is a solid element made of material that absorbs infrared heat, the infrared radiation typically being created by infrared lamps.
Resistance heating wire was one of the first applications of electricity, and many designs exist. However, current resistance heating wires are deficient because they cause significant pressure drops and do not transfer heat effectively.
Finned strip heating elements are a well known alternative form of electrical resistance heating element. Typically, they include an inner material which heats up when electricity is applied via induction heating and a thermally conductive outer casing with extended fins for the purpose of increasing the surface area, thus providing some increased heat transfer. However, they are deficient in many ways. For instance, their complex design makes them expensive to produce. Also, heat can travel along the fins instead of into the passing fluid. The fins typically extend well above the normal boundary layer and create significant turbulence, and so they do not control pressure drop well in relation to the benefit of increased heat transfer. In addition, the multiple parts necessitate that finned strip heating elements be significantly larger in profile than heating elements typically are, which may limit the applications for which they can be utilized.
Infrared heat has usually been used to heat a solid or liquid directly, the infrared radiation from the heat lamp being absorbed directly by the relatively dense solid or liquid. This is not effective when heating gas directly. For example, air at 25 degrees Celsius has 1/800th the density of water, so there is less absorption of infrared radiation in a gas because of the lower density. There are some known applications where the infrared radiation is used to heat a solid body which then transfers the heat to air. One known design is a flat plate which transfers the heat via natural convection, providing poor heat transfer. Another design employs round, ceramic heating elements which absorb the infrared heat from an infrared lamp, then transfer the heat via forced convection to a fluid flow passing transversely to the elements. However, round elements are not ideal for heat transfer and cause large pressure drops.
A need therefore exists for a solid heat transfer element with improved heat transfer which does not cause a significant increase in pressure drop relative to known solid heat transfer elements.